Inertial energy harvesting from ambient mechanical vibrations is a promising technology to enable next-generation wireless sensor nodes, which are self-powered, maintenance free, and thus truly autonomous. There have been a large number of micro and meso scale inertial harvesters reported up to date. Most can only operate at a single vibrational axis. Harvesting electrical energy from vibrations applied along any spatial direction can both improve their power output and extend the practical applications. One way to achieve this goal is by using three individual harvesters aligned along the three different axes assembled in a single package. This will, however, decrease the total power density and increase the overall cost due to the enlarged device size. Previously, single-transducer three-axis energy harvesters were reported only for electrostatic and electromagnetic resonators, although with very limited performance in terms of power output (16-25 nW) and power density (<125 nW/cm3/g2), resonance frequency (1.5-25 kHz), and frequency split (100-1000 Hz). Until now, only two-axis piezoelectric inertial harvesters have been reported, based on configurations such as asymmetric inertial mass, multiple mass-spring combinations, three-dimensional connecting member design, permanent-magnet and ball-bearing combination, and non-linear motion of a circular cantilever rod due to surrounding permanent magnet architecture. In addition to the limited number of operational axes, the architectures used in these devices require mostly three-dimensional structures with manual assembly, which prevent further device miniaturization. The present disclosure describes a piezoelectric transducer that can harvest electricity from mechanical energy in all three vibrational axes.
This section provides background information related to the present disclosure which is not necessarily prior art.